Problem: A circle with area $9\pi$ has a sector with a $168^\circ$ central angle. What is the area of the sector? ${9\pi}$ $\color{#9D38BD}{168^\circ}$ ${\dfrac{21}{5}\pi}$
Solution: The ratio between the sector's central angle $\theta$ and $360^\circ$ is equal to the ratio between the sector's area, $A_s$ , and the whole circle's area, $A_c$ $\dfrac{\theta}{360^\circ} = \dfrac{A_s}{A_c}$ $\dfrac{168^\circ}{360^\circ} = \dfrac{A_s}{9\pi}$ $\dfrac{7}{15} = \dfrac{A_s}{9\pi}$ $\dfrac{7}{15} \times 9\pi = A_s$ $\dfrac{21}{5}\pi = A_s$